DOI: 10.1002/chem.200701036

Dispirofluorene–Indenofluorene Derivatives as New Building Blocks forBlue Organic Electroluminescent Devices and Electroactive Polymers

Cyril Poriel,*[a] Jing-Jing Liang,[a] Jo/lle Rault-Berthelot,*[a] Fr2d2ric Barri3re,[a]

Nicolas Cocherel,[a] Alexandra M. Z. Slawin,[c] David Horhant,[a] Morgane Virboul,[a]

Gilles Alcaraz,[a, d] Nathalie Audebrand,[a] Laurence Vignau,*[b] Nolwenn Huby,[b]

Guillaume Wantz,[b] and Lionel Hirsch[b]

Introduction

During the last two decades, organic light-emitting diodes(OLEDs) have attracted considerable interest owing to their

promising applications in flat-panel displays that could re-place cathode-ray tubes or liquid-crystal displays.[1] The abil-ity to mass produce thin, efficient, bright displays from or-ganic polymers and small molecules that can supplantmodern liquid-crystal technology depends almost entirely onthe ability to create new materials that can undergo efficientelectroluminescence in a wide range of wavelengths. Interms of revenue, 2005 and 2006 have been the break-through years for the OLED technology in small- andmedium-size displays. However, its market penetration is ex-pected to remain modest in 2007.[2] This mainly arises fromthe rather short lifetime of organic materials despite therecent years improvements. Indeed, a number of approacheshave been tried for producing full-colour displays, for exam-ple, in fabricating red, green and blue pixels. However, theshorter lifetime of the blue-emitting materials is still one themain problem in OLED technology.[2] In this context, thequest for a material, for example, polymers[3–17] or smallmolecules,[18–46] with stable blue emission within an electrolu-minescent device continues to hold the attention of numberof research groups. It is of course not an easy task to find asmall molecule that not only possesses a very large bandgap, a large quantum yield in the solid state and that is alsostable to the harsh OLED environment. Fluorene (F) deriv-atives have been the most studied materials for blue emis-

Abstract: A series of new dispiro[fluor-ene-9’,6,9’’,12-indenoACHTUNGTRENNUNG[1,2b]fluorenes](DSF-IFs) has been synthesised. Thesenew building blocks for blue-light-emit-ting devices and electroactive polymerscombine indenofluorene (IF) andACHTUNGTRENNUNGspirobifluorene (SBF) properties. Wereport here our synthetic investigationstowards these new structures and theirthermal, structural, photophysical and

electrochemical properties. These prop-erties have been compared to those ofIF and SBF. We also report the anodicoxidation of DSF-IFs that leads to the

formation of non-soluble transparentthree-dimensional polymers. The struc-tural and electrochemical behaviour ofthese polymers has been studied. Thefirst application of these buildingblocks as new blue-light-emitting mate-rials in organic light-emitting diodes(OLED) is also reported.

Keywords: cyclic voltammetry · dis-pirofluorene–indenofluorene · fluo-rescence · light-emitting diodes ·polymers

[a] Dr. C. Poriel, J.-J. Liang, Dr. J. Rault-Berthelot, Dr. F. Barri<re,N. Cocherel, Dr. D. Horhant, M. Virboul, Dr. G. Alcaraz,Dr. N. AudebrandUMR CNRS 6226 “Sciences Chimiques de Rennes”UniversitD de Rennes 1, Bat 10C, Campus de Beaulieu35042 Rennes cedex (France)Fax: (+33)223-236732E-mail : cyril.poriel@univ-rennes1.fr

joelle.rault-berthelot@univ-rennes1.fr

[b] Dr. L. Vignau, Dr. N. Huby, Dr. G. Wantz, Dr. L. HirschUMR CNRS 5218 UniversitD de BordeauxENSCPB, 16 Avenue Pey-Berland, 33607 Pessac cedex (France)Fax: (+33)540-006631E-mail : l.vignau@enscpb.fr

[c] Prof. A. M. Z. SlawinSchool of Chemistry, University of StAndrewsSt Andrews, Fife KY16 9ST (UK)

[d] Dr. G. AlcarazLaboratoire de Chimie de Coordination (LCC)UPR CNRS 8241, Equipe A. O. C., 205 route de Narbonne31077 Toulouse Cedex 04 (France)

Supporting information for this article is available on the WWWunder http://www.chemeurj.org/ or from the author.

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sion, and this has led to many publications and patents.However, up to now, this has failed to produce an efficient,cheap and robust blue-light emitters.[2,33] Since the electronicand optical characteristics of the rigid F arise from its planarbiphenyl moieties, the structurally related compound, inden-ofluorene (IF), with a planar, longer conjugated p-terphenylmoieties has been suggested as a promising building block.Indeed, its incorporation into polymer or oligomer back-bones instead of F units has recently led to a strong en-hancement of OLED properties.[3,6,25,47–50] Moreover, it isknown that spiro-linked molecules such as spirobifluorene(SBF)[51] exhibit greater morphological stability and moreintense fluorescence, without any significant change in theirabsorption and fluorescence spectra compared to the non-spiro-linked parent compounds.[28] Another highly importantcharacteristic, which holds for most of SBF compounds, isthat they do not exhibit any emission bands beyond 500 nm.Such parasite emission bands are usually found in polyfluor-enes after annealing and are usually assigned to chain de-fects arising to partial oxidation of fluorACHTUNGTRENNUNGene units.[16] We thusdecided to desiGn a new family of chromophores that com-bine the IF and F properties within a single moleculethrough a spiro linkage. This new family of molecules hasbeen called dispirofluorene–indenofluorene (DSF-IF).[52]

The molecular design adopted in these molecules preserve

the p conjugation of the IF, which plays a prominent role inthe electronic, electrochemical and photophysical proper-ties; the introduction of the spiro configuration[51] gives themolecules a highly rigid structure.

In this work, as a development to our preliminary note,[53]

we first report our synthetic investigations and a newstraightforward route to the diiodoterphenyl as key buildingblock in the synthesis of DSF-IFs. The thermal, structural,photophysical and electrochemical properties of these mole-cules will be discussed, together with their first applicationin electroluminescent devices. In addition, these versatilemolecules also have the potential to form polymers by elec-trochemical oxidation leading to transparent electroactivedeposits with interesting electrochromic properties. Thestructural and electrochemical behaviours of these polymerswill be also developed.

Results and Discussion

Synthesis of DSF-IF derivatives

Retrosynthetic analysis : SBF can be considered as the join-ing of two fluorene units through a shared spiro carbon.First described by Clarkson and Gomberg in 1930,[54] it wasreadily obtained in a two-step synthesis from 2-iodobiphenyland fluorenone through a metal–halogen exchange reac-tion.[55–58] As DSF-IF can be considered as the joining of twoSBF moieties through a shared phenyl ring, it seemed rea-sonable to adopt a similar strategy. Our retrosynthetic ap-proach, based on a double lithium–halogen exchange reac-tion, is presented in Scheme 1 and involved 2,2’’-di-

ACHTUNGTRENNUNGiodo[1,1’;4’,1’’]terphenyl (2,2’’-DITP) as the key starting ma-terial. It should be noted that dihalogenated-p-terphenylsare not readily accessible and the target 2,2’’-diio-do[1,1’;4’,1’’]terphenyl has only been reported once so far.[59]

Synthesis of 2,2’’-DITP : As it was crucial in our strategy todevelop an efficient synthesis of 2,2’’-DITP at the multigramscale, two approaches were developed, both starting fromcommercially available 2-iodoaniline (Scheme 2, routes 1and 2). To avoid long and sophisticated multistep syntheses,the first method we developed involved original arylboronicacids bearing a triazene moiety in the ortho position readilyconvertible into iodide (Scheme 2, route 1).[52,53] 2-Iodoani-line (1) was diazotised by conventional means[60] and reactedin situ with pyrrolidine under basic conditions. The resultingo-iodoaryltriazene 2 was then converted into the corre-sponding boronic acid 3 by a lithiation/borylation sequenceinvolving n-butyllithium and trimethylborate followed byhydrolytic workup. Suzuki–Miyaura coupling[61] of o-triaze-nylboronic acid 3 with p-diiodobenzene (conditions: [PdCl2-ACHTUNGTRENNUNG(MeCN)2], tBu3P, K2CO3, dioxane/water) afforded 2,2’’-bis-ACHTUNGTRENNUNG(triazenyl)terphenyl (4) that was converted into 2,2’’-DITPin good yield by a subsequent heating with excess of methyl-ACHTUNGTRENNUNGiodide. The complete sequence was performed in 42% over-all yield.

Concerning the first step of the second route (Scheme 2,route 2), we decided to explore the protection of the aminogroup of the starting material 1, to avoid any solubility andreactivity issues in the subsequent Suzuki–Miyaura crosscoupling. The tert-Butylcarbamoyl (Boc) group was chosenas a protecting group (it is one of the most useful knownprotecting groups for amines).[62] The use of the non-nucleo-

Scheme 1. Retrosynthetic analysis of DSF-IF.

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philic, strong base sodium hexamethyldisilazane(NaHMDS)[63] prior the addition of the di-tert-butyldicar-bonate (Boc2O) leads cleanly to the corresponding tert-butyl-carbamoylated derivative 5. Reaction of 5 with 1,4-phenylenebisboronic acid under Suzuki–Miyaura cross-cou-pling conditions with [PdIICl2ACHTUNGTRENNUNG(dppf)]/CH2Cl2 (dppf=1,1’-bis(diphenylphosphino)ferrocene) as the catalyst andsodium carbonate as the base in a mixture of N,N-dimethyl-formamide and water (3:1) led to the terphenyl 6 in goodyield.[64] Deprotection of the amino groups was performedunder acidic conditions and diamino derivative 7 was quan-titatively obtained. Although the conversion of the 2-amino-biphenyl in 2-iodobiphenyl is an easy and high-yielding reac-tion,[65] it was more difficult in our case to perform the Sand-meyer reaction with two free amine units instead of one.Indeed, only a few examples are reported in the literaturefor the concomitant conversion of two amino groups intoiodine through a double Sandmeyer reaction. These reac-tions remain unclear and are difficult to reproduce; the re-sulting diiodides are mostly obtained in low yields.[4,59,66–68]

The target 2,2’’-DITP was obtained in 63% yield by using atenfold excess of KI as described by Holmes and co-work-ers.[9] In the solid state (Figure 1), the two iodophenyl rings

of 2,2’’-DITP lie on each side of the central phenyl ring (intrans positions to one another) with angles of around 548.

This second sequence (Scheme 2, route 2) was satisfactori-ly performed with an overall yield of 48%. This new route

is simple, can be performedunder mild conditions, is highlyadaptable, and is efficient forthe preparation of 2,2’’-DITP atthe multigram scale.

Synthesis of substituted 2,2’’-DITPs—2,2’’-DITPACHTUNGTRENNUNG(iPr)2 and2,2’’-DITP ACHTUNGTRENNUNG(oct)2 : Two other ter-phenyl derivatives substitutedwith isopropyl (2,2’’-DITP-ACHTUNGTRENNUNG(iPr)2) or octyl groups (2,2’’-DITP ACHTUNGTRENNUNG(oct)2) in the meta posi-tions of the biphenyl linkagewere prepared by followingroute 1 as previously report-ed.[53] However, as routes 1 and2 involved the same para-alkyl-substituted starting iodoanilineit was evident that route 2might also be used (Scheme 3).

Synthesis of DSF-IFs : With the three terphenyl 2,2’’-DITPsin hand, the lithium–iodine exchange with n-butyllithium inTHF at low temperature followed by quenching with fluor-ACHTUNGTRENNUNGenone gave the corresponding diols 8–10, which were finallyheated to reflux in acidic conditions to yield the correspond-ing DSF-IFs (Scheme 4).[53]

The moderate yields obtained in the lithium–halogen ex-change reaction may be partially explained by the systemat-ic formation of a byproduct identified by single-crystal X-ray diffraction as the monofluorenol 11 (Figure 2). This phe-nomenon has already been observed by Huang and co-workers in investigations of related compounds.[69] Depend-ing on the conditions, this monocoupling derivative may beformed in moderate (20%) to high yield (50%).

Physicochemical properties of DSF-IF derivatives: As DSF-IFs combine 9,9’-SBF and IF frameworks, it was of great in-terest to compare their physicochemical properties withthese two constituent building blocks. 9,9’-SBF was preparedaccording to literature procedures.[65,70,71] IF was prepared ina four step synthesis, by a modified Wang procedure (seedetails in the Supporting Information).[72]

Scheme 2. Synthesis of 2,2’’-DITP a) 1. NaNO2, AcOH/HCl, 0 8C; 2. C4H9N/KOH, H2O, 0 8C (95%); b) 1.nBuLi, Et2O, �78 8C; 2. B(OMe)3, �78 8C!RT; 3. H2O/NH4Cl (77%); c) 1,4-C6H4I2, K2CO3, [PdCl2(MeCN)2],tBu3P, dioxane/H2O, 80 8C (89%); d) MeI, 120 8C (64%); e) 1. NaHMDS, THF, RT; 2. Boc2O (84%); f) 1,4-C6H4(B(OH)2)2, [PdCl2(dppf)], Na2CO3, DMF/H2O, 90 8C (91%); g) TFA, CH2Cl2, 0 8C!RT (99%); h) 1.NaNO2, H2O/HCl, 0 8C; 2. KI/H2O, 0 8C!60 8C (63%).

Figure 1. Crystal structure from single-crystal X-ray data of 2,2’’-DITP.

Scheme 3. Synthesis of substituted 2,2’’-DITP(iPr)2 and 2,2’’-DITP(oct)2.

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Structural properties : The DSF-IFs are dispiro molecules with alinear antarafacial geometry.[69]

Single crystals of DSF-IF ACHTUNGTRENNUNG(iPr)2

were obtained by slow diffusionof hexane into a solution of thesample in CDCl3 and were ana-lysed by X-ray diffraction inorder to elucidate its molecularstructure and bulk-packingcharacteristics (Figures 3 and4).

The angles between the planeof indenofluorenyl moieties(through the central phenylring) and that of fluorenyl moi-eties (through the central cyclo-pentane ring) are 89.3 and 898,which indicates that the fluo-rene rings are almost perfectly

orthogonally linked through the spiro carbon. It also indi-cates that no additional deformation on these dispiro com-pounds is observed when comparing with a simple spirobi-fluorene X-ray structure.[57,73,74] The indenofluorenyl moietyis almost perfectly flat with only two distortions on eachside, probably caused by the two isopropyl substituents.

As indicated in the crystal packing diagram of DSF-IF-ACHTUNGTRENNUNG(iPr)2 presented in Figure 4, the fluorene rings lie on eachside and in the top and bottom faces of the indenofluoreneplane efficiently suppressing any interchromophore interac-tions. The plane-to-plane distance between two indenofluor-ene moieties was calculated to be 5.43 Q. These structuralfeatures may reduce the excimer formation in solid film asalready observed for similar structures.[75,76]

Thermal properties of DSF-IFderivatives : Thermal propertieswere examined using thermog-ravimetric (TGA) and differen-tial scanning calorimetry (DSC)analyses. The glass transition(Tg), melting transition (Tm),crystallisation (Tc) and decom-position (Td) temperatures aresummarised in Table 1. The Td

is defined as the temperature at which 5% loss occursduring heating.[51] As shown by the TGA curves presentedin Figure 5a, the three DSF-IF were highly stable as theyonly started to decompose around 360 8C for DSF-IF andDSF-IF ACHTUNGTRENNUNG(oct)2 and around 380 8C for DSF-IF ACHTUNGTRENNUNG(iPr)2. For com-

Scheme 4. Synthesis of DSF-IFs.

Figure 2. Crystal structurefrom single-crystal X-ray dataof the byproduct 11 (hydrogenatoms have been omitted forclarity).

Figure 3. Crystal structure from single-crystal X-ray data of DSF-IF(iPr)2 (hydrogen atoms have been omitted for clarity).

Figure 4. Crystal packing diagram of DSF-IF(iPr)2. Top: along the cstacking axis. Bottom: along the a stacking axis. The co-crystallised sol-vent (CDCl3) and the hydrogen atoms have been omitted for clarity.

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C. Poriel, J. Rault-Berthelot, L. Vignau et al.

parison, SBF[51] and IF,[3,48,77] which have been widely usedas efficient building blocks within materials for OLEDs,both start to decompose around 200 8C. Thus, the higherthermal stability of the new di-spiro DSF-IFs buildingblocks appears to be promising for incorporation as centralcore of polymers or oligomers. This stability may be due tothe presence of their rigid spiro-fused orthogonal bifluorenelinkages, as such spiro-configuration benefit has alreadybeen described in the literature.[78–81]

Figure 5b–d show the DSC heating curves of the threeDSF-IFs. In the case of DSF-IF ACHTUNGTRENNUNG(oct)2 (Figure 5d) an endo-thermic peak at 237 8C corresponding to the melting transi-tion (Tm) appeared during the first run. After cooling thesample down, a glass transition temperature Tg around 88 8Cwas observed during the second run. Further heating abovethe Tg resulted in the appearance of an exothermic peak(156 8C) due to crystallisation and finally the melting transi-tion again. A completely different behaviour was observedin the cases of DSF-IF (Figure 5b) and DSF-IF ACHTUNGTRENNUNG(iPr)2 (Fig-ure 5c). From room temperature to 300 8C no significantphase transition (including Tg) was detected neither forDSF-IF nor for DSF-IF ACHTUNGTRENNUNG(iPr)2. This phenomenon has beenalready observed for similar bulky structures such as spiro-fluorene–anthracene derivatives.[3] Such thermal behaviouris of importance to improve the lifetime of OLEDs.[2] Thus,in term of thermal properties, DSF-IF and DSF-IF ACHTUNGTRENNUNG(iPr)2 arepromising for practical use in OLEDs.

Electrochemical properties of DSF-IF derivatives—anodicbehaviour : DSF-IF oxidation (Figure 6A and B) occursalong two processes which have maxima at E1 (1.47 V) andE2 (1.95 V). The E1 and E2 potential values are similar forDSF-IF ACHTUNGTRENNUNG(oct)2 and DSF-IF ACHTUNGTRENNUNG(iPr)2 (Table 2). This shows thatthe presence of alkyl groups on the indenofluorenyl moietiesof DSF-IFs has only a weak influence on the oxidation po-tential. The donor inductive effect leads to an E1 shift of�30 mV for octyl and �100 mV for isopropyl groups. Forthe three DSF-IFs, the intensities of E1 and E2 waves are ina ratio of 1:4 electrons. This may correspond to a first one-electron oxidation at E1 followed by a four-electron oxida-tion at E2. It should be noted that only the E1 wave is rever-sible (Figure 6A). Figure 6C and E present the CVs record-ed along IF and 9,9’-SBF oxidation in a similar potentialrange. The anodic oxidation of IF and 9,9’-SBF occurs in

two waves with maxima E1 at 1.31 and 1.69 V and E2 at 1.81and 1.86 V, respectively. For IF the potential shift betweenE1 and E2 is around 0.5 V whereas for 9,9’-SBF the shift be-tween the two peaks is only 0.17 V. The intensity ratio of E1

Table 1. Thermal properties of the DSF-IFs, IF and SBF [8C].[a]

Td[b] Tg

[c] Tc[d] Tm

[e]

DSF-IF 355 n.o. n.o. n.o.DSF-IF(iPr)2 382 n.o. n.o. n.o.DSF-IF(oct)2 366 88 156 237IF 200 n.d. n.d. n.o.SBF 204 n.d. n.d. 204

[a] n.d.: not determined, n.o.: not observed. [b] Td: decomposition tem-perature (5% loss). [c] Tg: glass transition temperature, determined byDSC in second heating cycle. [d] Tc : crystallisation transition tempera-ture, determined by DSC in second heating cycle. [e] Tm: melting point,determined by DSC in first heating cycle and melting point apparatus.

Figure 5. Thermal analysis of DSF-IFs. a) TGA curves for DSF-IF (g);DSF-IF(iPr)2 (c) and DSF-IF(oct)2 (b). DSC curves, first run (b)and second run (c) for b) DSF-IF; c) DSF-IF(iPr)2 and d) DSF-IF(oct)2.

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and E2 waves is 1:3 for IF and 1:1 for 9,9’-SBF. Figure 6Dand F show that the wave E1 is reversible in the case of IFand irreversible for 9,9’-SBF. As already observed for DSF-IFs, iterative cycles in the E1 potential range of IF do notshow any modification of the CV nor of the electrode sur-face. For 9,9’-SBF, iterative cycles leads to a slow electrode-position process.[82,83] Finally, a comparison of the first oxida-tion peak of IF with the one of DSF-IF shows that IF ismore easily oxidised than the indenofluorenyl unit in DSF-IF. The positive shift of 0.16 V from IF to DSF-IF oxidationmay result from the electron-withdrawing effect of thespiro-linked fluorenyl units rendering the indenofluorenylpart of DSF-IF more difficult to oxidise. This might be seenas a proof of the spiroconjugation already described from atheoretical point of view in the literature.[84–91] All these ob-servations lead us to conclude that the oxidation of DSF-IFcompounds occur first through a one-electron oxidation ofthe indenofluorenyl part of the molecule (E1) followed bythe oxidation of the spiro-linked fluorenyl units (E2).

Electrochemical properties of DSF-IF derivatives—cathodicbehaviour : The cathodic behaviour of DSF-IFACHTUNGTRENNUNG(oct)2 is pre-sented in Figure 7 together with the reduction of IF, F and9,9’-SBF. In DMF, the DSF-IFs present a reversible reduc-tion wave around �2.4 V (see E1 values reported inTable 2). As expected, the inductive donor effect of thealkyl groups in DSF-IF ACHTUNGTRENNUNG(oct)2 and DSF-IF ACHTUNGTRENNUNG(iPr)2 leads to ashift of E1 towards more negative potentials relative toDSF-IF.

IF reduction (E1 =�2.55 V) is slightly more difficult thanthat of DSF-IFs one. As already observed in the oxidationprocess, the spiro-linked fluorenyl groups have an electron-withdrawing effect on the indenofluorenyl part of the mole-cules through the spiro carbon atoms. DSF-IFs exhibit asecond, quasi-reversible, reduction wave at more negativepotentials close to the F and 9,9’-SBF reduction potentials(see the broken line of DSF-IF ACHTUNGTRENNUNG(oct)2 reduction). This secondreduction wave leads to the reduction of the spiro-linkedfluorenyl units of the DSFIFs.

Theoretical calculations[92] are consistent with the electro-chemical measurements pointing to an indeno-based pri-mary oxidation and reduction in DSF-IFs, as shown by thecalculated nature of the frontier molecular orbitals of DSF-

Figure 6. Cyclic voltammetry in presence of A),B) DSF-IF (3R10�3m);

C),D) IF (2R10�3m); E),F), 9,9’-SBF (5R10�3

m) in CH2Cl2 (Bu4NPF6

0.2m) for DSF-IF and 9,9’-SBF and in CH3CN+CH2Cl2 (v/v) (Bu4NPF6

0.1m) for IF; working electrode: Pt disk diameter 1 mm; sweep-rate100 mVs�1. The potential limit was 0.4–2.4 V in A; 0.4–1.7 V in B; 0.2–2.3 V in C; 0.3–1.5 V in D; 0.8–2.24 V in E; 0.37–1.7 V in F. The currentscale S is equal to 2 in D, 4 in B, 8 in A and C and 16 in E and F.

Table 2. Electrochemical data for DSF-IFs, IF, SBF and F.

Oxidation potential[V] vs. SCE[a]

Reduction potential[V] vs. SCE[a]

E1 E2 Eoxonset E1 Ered

onset

DSF-IF 1.47 1.95 1.36 �2.32 �2.23DSF-IF(oct)2 1.44 1.99 1.30 �2.48 �2.35DSF-IF(iPr)2 1.37 1.95 1.26 �2.48 �2.33IF 1.31 1.81 1.22 �2.55 �2.41SBF[82,83] 1.69 1.86 1.54 �2.73 �2.58F[82,83] 1.62 – 1.48 �2.87 �2.71

[a] Obtained from CVs recorded in CH2Cl2 +Bu4NPF6 (0.2m) in oxida-tion and in DMF+Bu4NPF6 (0.1m) in reduction. Figure 7. Cyclic voltammetry of DSF-IF(oct)2 (5.78R10�4

m), IF (2.91R10�3

m), F (6.32R10�3m) and 9,9’-SBF (2.4R10�3

m) in DMF (Bu4NPF6

0.1m), working electrode: Pt disk diameter 1 mm, sweep-rate 100 mVs�1.The potential limit was �0.58 V to �2.6 V for DSF-IF(oct)2; �2.72 V forIF; �3.1 for F and �2.94 V for 9,9’-SBF. The current scale S is equal to0.4 (c) and 0.8 (a) for DSF-IF(oct)2; 4 for IF and 9,9’-SBF and 8for F.

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IF in Figure 8. Indeed, we note the indenofluorenyl charac-ter of the HOMO and LUMO and the spirofluorenyl char-acter of the two pairs of quasi-degenerate LUMO+1,LUMO+2 and HOMO�1, HOMO�2.

Electrochemical and optical band gap : Following the workof Jenekhe,[95] we did an experimental estimation of theelectron affinity (EA) or lowest unoccupied molecular orbi-tal (LUMO) and of the ionisation potential (IP) or highestoccupied molecular orbital (HOMO) from the redox data(Table 3). The LUMO level was calculated from: LUMO(eV)=�[Ered

onset (vs SCE)+4.4] and the HOMO level from:HOMO (eV)=�[Eox

onset (vs SCE)+4.4], based on an SCEenergy level of 4.4 eV relative to the vacuum. The electro-chemical gap DEel obtained as Eox

onset�Eredonset (in eV) was also

compared to the optical band gap calculated from the ab-sorption edge of the UV/Vis absorption spectra using theformula DEopt (eV)=hc/l.

The calculated band gaps from electrochemical data ofDSF-IFs are consistent with the measured optical band gaps

with only a small deviation (0.2 eV or less). These values arealso qualitatively consistent with the theoretical values ob-tained with DFT calculations: although the HOMOs and es-pecially the LUMOs energies are overestimated by the DFTmethod (ca. 0.1–0.4 and 0.9–1 eV respectively), the experi-mental trend in the frontier molecular orbital energy and as-sociated band gap is well reproduced theoretically. TheDSF-IFs band gap appears to be wide (3.5/3.6 eV) with aHOMO level around �5.7 eV and the LUMO level around�2.1 eV. SBF and F have a larger band gap (larger than4 eV) with a deeper HOMO and a higher LUMO. As a con-sequence, the DSF-IFs compounds are interesting in this re-spect, for electroluminescent devices, since their energylevel better fit the cathode and anode work function (seeFigure 13 in a later section).

Anodic electrodeposition—synthesis of electroactive poly-mers : The first oxidation of DSF-IFs involves the indeno-fluorenyl part of the molecules in a one-electron process(vide supra), whereas the second oxidation occurs on thetwo spiro-linked fluorenyl units. This second process occursin a potential range slightly more positive than the oxidationpotential of SBF and F oxidation (Table 2). These two com-pounds are known to undergo electropolymerisation pro-cesses[82,83,97–99] and DSF-IFs present the same behaviour.Indeed, recurrent sweeps between 0.5 and E2 lead to gradualmodification of the CVs and to the modification of the elec-trode surface by an insoluble transparent deposit. The de-posits derived from DSF-IFs are three-dimensional com-pounds with high electrochemical stability and interestingelectrochromic behaviour (see Figure 9).

Oxidation on transparent ITO-glass electrodes, allowedthe observation of the intense blue DSF-IF radical cationsgenerated at E1 and the pink radical cations generated at E2.The observation of these colourations allows us to assertthat DSF-IF polymerisation occurs in good yield as one ob-served no diffusion of coloured species in solution at the vi-cinity of the electrode along the electrodeposition process.Upon reduction at 0.5 V, the deposit became instantaneouslytransparent.

Coulometric measurements recorded along DSF-IF oxida-tion (see details in the Support-ing Information) show that thep-doping level, called m in thiswork, of the spiro-linked fluo-rene units is between 0.7 and 1electron. This value is equiva-lent to the one of poly(9,9’-SBF) but higher than the onepoly(F), that is, 0.3 electrons.

The three poly(DSF-IFs)present a similar electrochemi-cal behaviour in terms of onsetoxidation potential, potentialrange of stability and p-dopinglevel. This shows that the sub-stitution of the indenofluorenyl

Figure 8. Sketch of DSF-IF frontier molecular orbitals from Gaussian03B3LYP/6–31G* calculations.[92–94]

Table 3. Molecular frontier orbital energy and HOMO/LUMO gaps of DSF-IFs, IF, SBF and F from electro-chemical, optical and theoretical data.

HOMO[eV][a]

LUMO[eV][b]

HOMO[eV][c]

LUMO[eV][c]

DEel

[eV][d]DEopt

[eV][e]DEcalc

[eV][f]

from redox data from calculations

DSF-IF �5.76 �2.17 �5.41 �1.23 3.59 3.51 4.18DSF-IF(oct)2 �5.70 �2.05 – – 3.65 3.47 –DSF-IF(iPr)2 �5.66 �2.07 �5.35 �1.19 3.59 3.44 4.16IF �5.62 �1.99 �5.43 �1.13 3.63 3.61 4.30SBF �5.94 �1.82 �5.69 �0.84 4.12 3.91 4.85F �5.88 �1.69 �5.81 �0.77 4.19 3.97 5.04

[a] Calculated from the onset oxidation potential. [b] Calculated from the onset reduction potential. [c] Gauss-ACHTUNGTRENNUNGian 03 B3LYP/6–31G* calculation:[92,94] a SCRF solvation model[96]was applied to the optimised geometry ofeach model using dichloromethane and acetonitrile for the determination of the HOMO and LUMO energyrespectively. [d] Calculated as DEel =Eox

onset�Eredonset. [e] Calculated from the absorption edge of the absorption

spectrum using DEopt =hc/l. [f] DEcalc = jHOMO�LUMO j from theoretical calculations.

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part of the molecule by an alkyl group does not influencethe p-doping process of the polyfluorenyl chains. Figure 9B–D present the anodic behaviour of poly(DSF-IF) deposits.

In B, the deposit was obtainedalong the CVs recorded Fig-ure 9A. The onset oxidation po-tential of the deposit is at0.94 V, negatively shifted of420 mV when compared to theEox

onset of DSF-IF signing an ex-tension of the conjugationlength in the polymer. The de-posit is electrochemically stable(reversibility of the p-dopingprocess higher than 95%) in arather large potential range (upto more than 2 V). CVs report-ed Figure 9C,D were recordedfor thin deposits of poly(DSF-IF) prepared at different po-tentials (E=1.9 and 2.3 V, see the Supporting Information).For the deposit prepared at the lowest potential (Figure 9C),the first wave is associated with the oxidation of the indeno-fluorenyl part of the polymer and is followed by three otherwaves that might be attributed to the different oxidationlevels of the polyfluorenyl chains. For the deposit preparedat higher potential (Figure 9D), the oxidation of the indeno-fluorenyl part appears as a shoulder before the two oxida-tion waves of the polyfluorenyl chains. Coulometric meas-urements were also performed along poly(DSF-IF) p-dopingprocess between 0.5 and 2.1 V and show that the p-dopinglevel, called m’ in this work, of the spiro-linked fluorene

units is between 1 and 1.7. The higher m’ values, relative tothe m values, are due to the higher potential reached alongthe p-doping process. The m’ values show the high-energystorage potential of the poly(DSF-IF).

Electrochromic properties of these polymers were ob-served when switching their oxidation state from their neu-tral to their p-doped level. The deposit changes colour fromtransparent to purple with a short switching time and a goodstability of the switch measured along chronoamperometricexploration. As the current keeps more than 95% of its ini-tial value (after 1000 cycles), these polymers possess highlyinteresting electrochromic properties.[100]

In terms of mechanism, and keeping in mind the electro-ACHTUNGTRENNUNGpolymerisation process of F and 9,9’-SBF already describedin literature,[99] we expected that the polymerisation of DSF-IF begins by the one-electron oxidation of the indenofluor-enyl part of the molecule at E1, followed by the oxidation ofthe spiro-linked fluorenyl units at E2. The cation radical ofthese units are quickly involved in dimerisation processes.The formation of the C�C bond leads to new dihydrodimer–dications that lose protons to form the final dimers. Theelectrogenerated dimers are easier to oxidise than the start-ing ACHTUNGTRENNUNGmonomer and give new dimer radical cations at the levelof the monomer oxidation potential. Then, these dimer radi-cal cations will repeat the coupling step to form trimers, tet-ramers and so forth. The reduction of the deposit at 0.5 Vlead to the charge neutralisation and the formation of theneutral poly(DSF-IFs) (Scheme 5). This scheme, which is an

ideal representation of the polymer network, is however in-formative as it shows that the aromatic polyfluorenyl chainsare well organised in parallel wires, with no evident inter-chain communication between one another due to the in-denofluorenyl groups.

Optical properties of DSF-IF derivatives

UV/Vis absorption spectra of the DSF-IFs : The UV/Vis ab-sorption of DSF-IFs were first studied and compared withthe UV/Vis absorption of F, SBF and IF (Table 4, Figure 10,top). For solubility purposes, these compounds were all stud-ied in solution in CH2Cl2. F and SBF have similar absorption

Figure 9. Cyclic voltammetry in CH2Cl2 (Bu4NPF6 0.2m). A) DSF-IF (3R10�3

m), ten sweeps between 0.5 and 2.22 V, working electrode: Pt disk di-ameter 1 mm. B)–D) working electrode: Pt disk diameter 1 mm modifiedby a deposit of poly(DSF-IF). For B, the electrodeposition was per-formed along the CVs recorded in A; for C and D the electrodepositionwas performed by oxidation of a 3R10�3

m solution of DSF-IF in CH2Cl2(Bu4NPF6 0.2m) at fixed potential: 1.9 V for C and 2.3 V for D with Qt,the amount of charge for the formation, equal to 2R10�4C. The potentiallimit was 0.24 to 2.1 V in B and 0.5 to 2.1 V in C and D. The currentscale S is equal to 40 in A and B and to 16 in C and D. Sweep-rate:100 mVs�1.

Scheme 5. Schematic representation of DSF-IFs electrodeposition.

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C. Poriel, J. Rault-Berthelot, L. Vignau et al.

spectra, displaying two sharp bands (290 and 301 for F, 297and 309 nm for SBF) in addition to a broad one around250–265 nm. The electronic spectra of DSF-IFs present ab-sorption bands around 230, 254, 300, 310 as for F and SBFand three additional bands around 330–335, 335–340 and345–350 nm. For DSF-IF we precisely observed these threebands at 330, 337 and 345 nm, which are in accordance withthe absorption bands of IF at 319, 328 and 334 nm,[72] butbathochromically shifted by about 10 nm. This shift may beassigned to the influence of the spiro-linked F rings on theIF moieties. This effect may arise from the interactions be-tween the two orthogonally linked p systems, that is, spiro-conjugation, as already observed with CV.

UV/Vis absorption spectra ofthe polymers : Poly(DSF-IF)spectrum exhibits a large ab-sorption band between 300 and350 nm due the more extendedconjugation than in the DSF-IFmonomer (Figure 10, bottom).Such a large band was also ob-served as the main absorptionband in poly(SBF).[82,83] We alsoobserved two sharp peaks at

312 and 346 nm. These absorptions fit well with those ofDSF-IF (Figure 10, top) and confirm the presence of DSF-IF patterns in the polymeric network.

Emission spectra : The photoluminescence of DSF-IFs wasstudied in cyclohexane and compared with SBF and IF inorder to evaluate the efficiency of these molecules as keystructures for further OLED applications (Figure 11 and

Table 4). The central building block IF exhibits two mainemissions (lexc =334 nm) with maxima at 339 and 356 nm(Figure 11). DSF-IF after excitation at 344 nm shows twosimilar emissions at 347 and 366 nm. This 10 nm shift, al-ready observed in the UV/Vis absorption (Figure 10, top)may be attributed to the interaction between the F rings andthe central IF ring through the spiro-carbon. DSF-IF(iPr)2

and DSF-IF(oct)2 exhibit the same behaviour with emissionat 351 and 370 nm. The small Stokes shift observed forDSF-IFs is consistent with the rigidity observed in the solidstate structure. fsol was determined by using standard proce-dures with quinine sulphate dihydrate as reference.[72] IF ex-hibits a quantum yield of 61%, slightly lower than the re-sults reported by Wang.[72] The three DSF-IFs appear to behighly efficiently fluorescent with high quantum yields ofaround 65%.

Organic light-emitting diodes (OLEDs) using DSF-IFs asthe emitting layer: As the DSF-IF core may be interesting

Table 4. Photophysical properties

lAbs [nm][a] lExc [nm] lEm [nm][a,b] fsol [%][c]

DSF-IF 231, 254, 300, 311, 330, 337, 345 344 347, 356, 366 62DSF-IF(iPr)2 231, 254, 300, 311, 333, 340, 348 348 351, 359, 370 66DSF-IF(oct)2 228, 254, 301, 312, 334, 341, 349 348 351, 359, 370 66IF 228, 235, 289, 302, 319, 328, 334 334 339, 347, 356 61SBF 229, 252, 297, 309 309 312, 323 20

[a] Measured in dichloromethane. [b] Measured in cyclohexane for all compounds except for IF (decalin).[c] The relative quantum yield was measured with reference to quinine sulphate in 1n H2SO4 (f=0.546).

Figure 10. Top: UV/Vis spectra of DSF-IF (a), F (g), SBF (c)and IF (d) in solution in CH2Cl2 (10�5

m). Bottom: UV/Vis spectra ofDSF-IF in solution in CH2Cl2 (c), poly-DSF-IF deposited on an ITOelectrode plunged in CH2Cl2 (a).

Figure 11. Emission spectra: 6R10�7m solutions of DSF-IF (g), DSF-

IF(iPr)2 (d) DSF-IF(oct)2 (c) in cyclohexane, IF (a) in decalin.

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FULL PAPERElectroluminescent Devices

as a new building block for electroluminescent devices, itseemed of great interest to study its behaviour in OLEDs.DSF-IF, DSF-IF(iPr)2 and DSF-IF(oct)2 exhibited similarelectroluminescence properties therefore only results onDSF-IF(iPr)2 are presented. Basic OLED structures withITO as the anode, poly(3,4-ethylene dioxythiophene) dopedwith poly(styrene sulfonate): PEDOT/PSS as the hole inject-ing layer (HIL), DSF-IF(iPr)2 as the emitting layer (EML)and Ca as the cathode were first fabricated and character-ised (Figure 12a). The associated band energy diagram of

that structure is presented in Figure 12c. The LUMO ofDSF-IF(iPr)2 is very low (�2.1 eV), therefore a cathodewith a low work function needs to be used in order toenable charge injection into the DSF-IF(iPr)2 layer. Calciumseemed the most appropriate available metal for that pur-pose with a work function of �2.9 eV. LiF/Al was alsotested but resulted in lower efficiency OLEDs.

The normalised electroluminescence spectrum recordedfor ITO/PEDOT/DSF-IF(iPr)2/Ca devices (Figure 13) exhib-its two main emission peaks in the blue region at 399 and416 nm. Two other contributions are found at 483 and587 nm. The chromatic coordinates calculated from the elec-troluminescence spectrum in the CIE 1964 chromaticity dia-gram are (0.21; 0.16). These coordinates correspond to ablue colour as can be seen on Figure 13.

Current-density–voltage–luminance characteristics of theITO/PEDOT/DSF-IF(iPr)2/Ca OLEDs are presented inFigure 14 (top). The turn on voltage appears around 7 V.The luminance of the device reaches 200 Cdm�2 at 15 V andfor a current density of 22 mAcm�2. In terms of efficiency,the devices reach 0.9 CdA�1 and 0.19 LmW�1 at 200 Cdm�2

(Figure 14, bottom), which is promising for single-layer blueOLEDs.

To improve the performances of the DSF-IF(iPr)2-basedOLEDs a hole transport layer (HTL), N,N’-diphenyl-N,N’-bis(3-methylphenyl)-[1,1’-biphenyl]-4,4’-diamine (TPD) wasinserted between the anode and the emitting layer (Fig-ure 12b and d).[101] The HOMO energy level of TPD lies be-tween those of PEDOT and DSF-IF(iPr)2. This should resultin an easier hole injection into the DSF-IF(iPr)2 layer. How-ever the comparison of the voltage–luminance characteris-tics of the OLEDs with and without TPD (Figure 15) revealpoorer performances of the TPD/DSF-IF(iPr)2-based deviceboth in terms of luminance and efficiency. The TPD-basedOLEDs reach a maximum efficiency of 0.4 CdA�1 versus0.9 CdA�1 for the single-layer DSF-IF(iPr)2-only device(vide supra). Furthermore the threshold voltage is slightlyincreased. This can be due to the additional TPD layer,which causes a global increase of the organic layer thicknessand results in a higher turn-on voltage. Moreover, theLUMO level of TPD (�2.5 eV) lies below that of DSF-IF(iPr)2 (�2.1 eV). As a consequence, when electrons are in-jected into the DSF-IF(iPr)2 layer they are not confinedwithin that layer as there is no energetic barrier to cross atthe DSF-IF(iPr)2/TPD interface. The use of an electron

Figure 12. a),b) Structures of the investigated OLEDs. HIL, HTL andEML correspond to the hole-injecting layer, the hole-transport layer andthe emitting layer, respectively. c),d) Schematic representation (beforecontact) of the energetic structure associated with the investigated devi-ces.

Figure 13. Electroluminescence spectrum of ITO/PEDOT/DSF-IF(iPr)2/Ca device with the corresponding colour placed on the CIE 1964 chroma-ticity diagram.

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blocking layer with a LUMO level significantly above�2.1 eV would improve the confinement of electrons. Simi-larly, holes are not confined within the DSFIF(iPr)2 layer.Therefore, some charge carriers (electrons and holes) cancross the emitting layer without radiative recombination.This causes a decrease of efficiency.

To enhance injection electrons and block holes, Alq3 isoften inserted between the emitting layer and the cathode.A ITO/PEDOT/TPD/DSF-IF(iPr)2/Alq3/Ca device has beenmade but its electroluminescence spectra showed a contribu-tion of Alq3. Indeed, the LUMO level of Alq3 (�3.1 eV)lies below that of DSF-IF(iPr)2 (�2.1 eV) as well as belowthe work-function of Ca (�2.9 eV). It means that electronsare confined in the Alq3 layer instead of in the emittinglayer. Moreover, as the HOMO level of Alq3 (�5.6 eV) liesslightly above that of DSF-IF(iPr)2 (�5.7 eV), no holeblocking effect can be observed. This confirms that Alq3 isnot a suitable material to enhance both electron injectionand hole-blocking processes in those systems. Similarly, Wuand co-workers did not observe any hole blocking in PPVderivatives.[102] The use of a electron and/or hole-blockinglayers able to confine charge carriers in the DSF-IF(iPr)2

layer appears essential for multilayer devices.

Conclusion

In summary we have synthesised a series of new lumino-phores combining one indenofluorenyl unit and two spiro-linked fluorenyl units. These molecules, called DSF-IFs,have been prepared by short efficient syntheses through akey di-iodinated terphenyl intermediate (2,2’’-DITP). Webelieve this intermediate might be of great interest for theelaboration of other dispiro compounds for organic opto-ACHTUNGTRENNUNGelectronics. Their electrochemical behaviour has been stud-ied and compared to their constituent building blocks, thatis, IF and SBF, to evaluate their HOMO/LUMO levels andto understand their electronic properties. These results havebeen confirmed by DFT calculations. The thermal and pho-tophysical properties of DSF-IFs have been estimated andappeared to be promising for OLED applications. Theseversatile molecules may be also polymerised through thefluorene cores, and lead to electroactive three-dimensionalmaterials with interesting optical and electrochromic proper-ties. The preliminary studies carried out on DSF-IFs for theOLED application led to interesting and promising proper-ties for blue emitters. Indeed, DSF-IF(iPr)2 exhibits goodperformances when used in a single-layer device. The effi-ciencies could even be further increased with the use ofcharge-blocking layers. Further optimisations of the devicesare currently in progress and will be reported in due course.

Experimental Section

General : Commercially available reagents and solvents were used with-out further purification other than those detailed below. Dichloro-

Figure 14. Top: I-V-L characteristics. Bottom: luminous and energetic ef-ficiencies of an ITO/PEDOT/DSF-IF(iPr)2 (30 nm)/Ca OLED.

Figure 15. Top: Luminance–voltage characteristics. Bottom: luminous ef-ficiency of OLEDs with the following structures: ITO/PEDOT/DSF-IF(iPr)2 (30 nm)/Ca and ITO/PEDOT/TPD (20 nm)DSF-IF(iPr)2

(30 nm)/Ca.

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ACHTUNGTRENNUNGmethane was distilled over calcium hydride prior to use. THF and cyclo-hexane was distilled from sodium/benzophenone. Light petroleum refersto the fraction with b.p. 40–60 8C.

Synthesis : Reactions were stirred magnetically, unless otherwise indicat-ed. Analytical thin-layer chromatography was carried out using alumini-um-backed plates coated with Merck Kieselgel 60 GF254 and visualisedunder UV light (at 254 and/or 360 nm). Chromatography was carried outwith silica 60 A CC 40–63 mm (SDS). 1H and 13C NMR spectra were re-corded on Bruker 200 and 300 MHz instruments (1H frequencies, corre-sponding 13C frequencies are 50 and 75 MHz); chemical shifts were re-corded in ppm and J values in Hz. In the 13C NMR spectra, signals corre-sponding to CH, CH2 or Me groups, assigned from DEPT, are noted; allothers are C. The residual signals for the NMR solvents are: CDCl3;7.26 ppm for the proton and 77.00 ppm for the carbon, CD3OD;3.31 ppm for the proton and 49.05 ppm for the carbon, (CD3)2SO;2.50 ppm for the proton and 39.43 ppm for the carbon. The following ab-breviations have been used for the NMR assignment: s for singlet, d fordoublet, t for triplet, q for quintet and m for multiplet. “br” abbreviationmeans that the signal is broad. High-resolution mass spectra were record-ed at the CRMPO (Rennes). Substituted 2,2’’-DITPs and the correspond-ing DSF-IFs were prepared according literature procedures.[53] 9,9’-SBFwas prepared according literature procedures.[65,70, 71] IF was prepared in afour-step synthesis by a modified Wang procedure (see details in Sup-porting Information).[72]

(2-Iodophenyl)carbamic acid tert-butyl ester (5): Sodium bis(trimethyl-ACHTUNGTRENNUNGsilyl)amide (8.2 mL, 16.4 mmol) was added dropwise to a stirred solutionof 1 (1.8 g, 8.2 mmol) in dry THF (7.5 mL) at room temperature underan argon atmosphere. After 25 min, di-tert-butyldicarbonate (1.9 g,8.2 mmol) was added over 5 min by syringe. The reaction mixture wasstirred at room temperature for 2 h. Water (50 mL) was then added, andthe resulting mixture was extracted with dichloromethane (3R50 mL).The organic layer was washed with a saturated aqueous solution ofsodium chloride (50 mL), dried (MgSO4), and evaporated in vacuo. Pu-rification by column chromatography on silica gel eluting with ethyl ace-tate/light petroleum (1:9) gave compound 5 (2.2 g, 84%) as a yellow/orange oil. 1H NMR (300 MHz; CDCl3): d=8.04 (dd, J=7.5, 1.5 Hz, 1H;ArH), 7.74 (dd, J=7.5, 1.5 Hz, 1H; ArH), 7.31 (td, J=7.5, 1.5 Hz, 1H;ArH), 6.82 (s, 1H; NH), 6.76 (td, J=7.5, 1.5 Hz, 1H; ArH), 1.54 ppm (s,9H; Me); 13C NMR (75 MHz; CDCl3): d=152.5 (C=O), 138.8 (CH),138.77 (C), 129.1 (CH), 124.6 (CH), 120.1 (CH), 88.7 (C-I), 81 (C),28.3 ppm (CH3); HRMS (EI): m/z calcd for C11H14INO2: 319.00693 [M]+ ;found: 319.0038.

2,2’’-Di-tert-butylbiscarbamate[1,1’:4’,1’’] terphenyl (6): Sodium carbonate(3.3 g, 31.5 mmol) dissolved in water (7 mL) was added to a solution oftert-butyl (2-iodophenyl)carbamate 5 (2.7 g, 8.5 mmol), 1,4-phenylene bis-boronic acid (0.5 g, 3.2 mmol) and 1,1’-bis(diphenylphosphino)ferrocenepalladium(II)dichloride dichloromethane complex (0.1 g, 0.1 mmol) inDMF (22 mL) at room temperature. The Schlenk tube was degassed, andthe mixture was allowed to stir at 90 8C for 12 h under an argon atmos-phere. The reaction mixture was then quenched with water (100 mL) andextracted with ethyl acetate (4R50 mL). The combined organic layerswere washed with a saturated aqueous solution of sodium hydrogencar-bonate (50 mL), dried (MgSO4) and evaporated in vacuo. Purification bycolumn chromatography on silica gel eluting with ethyl acetate/light pe-troleum (1:10) afforded compound 6 (1.3 g, 91%) as a colourless solid.M.p. 140–142 8C (acetonitrile); 1H NMR (300 MHz; CDCl3): d=8.10 (d,J=8.3 Hz, 2H; ArH), 7.50 (s, 4H; ArH), 7.37 (td, J=8.3, 1.5 Hz, 2H;ArH), 7.26 (dd, J=8.3, 1.5 Hz, 2H; ArH), 7.14 (td, J=8.3, 1.5 Hz, 2H;ArH), 6.57 (s, 2H; NH), 1.48 ppm (s, 18H; Me); 13C NMR (75 MHz;CDCl3): d =152.9 (C=O), 137.9 (C), 135.2 (C), 131 (C), 130.3 (CH), 129.9(CH), 128.6 (CH), 123.4 (CH), 120.4 (CH), 80.6 (C), 28.3 ppm (Me); IR(KBr): n =3250 (NH), 3028, 2978, 2931, 2870, 2815, 2761, 2715, 2284,2205, 1930, 1915, 1700 (CO), 1581, 1529, 1476, 1448, 1391, 1366, 1304,1289, 1245, 1164, 1040, 1036, 1007 cm�1; HRMS (EI): m/z calcd forC28H32N2O4·CO2C4H8: 360.18378 [M�CO2C4H8]

+ ; found: 360.1861.

1,1’:4’,1’’-Terphenyl-2,2’’-diamine (7): Trifluoroacetic acid (17.0 mL,229.0 mmol) was added to a solution of compound 6 (1.8 g, 3.9 mmol) indichloromethane (200 mL) at room temperature. The reaction mixture

was allowed to stir at room temperature for 4 h and was then cooled to0 8C and carefully neutralised (pH�7–8) with a saturated aqueous solu-tion of sodium hydrogencarbonate. The resulting mixture was extractedwith dichloromethane (3R50 mL). The organic layer was dried (MgSO4)and evaporated in vacuo to give compound 7 (1.1 g, 99%) as a colourlesssolid. M.p. 212 8C (dichloromethane/hexane); 1H NMR (300 MHz;CDCl3): d=7.55 (s, 4H; ArH), 7.21–7.15 (m, 4H; ArH), 6.88–6.78 (m,4H; ArH), 3.42 ppm (br s, 4H; NH); 13C NMR (75 MHz; CDCl3): d=

143.5 (C), 138.3 (C), 130.4 (CH), 129.4 (CH), 128.5 (CH), 137.1 (C),118.7 (CH), 115.6 ppm (CH); HRMS (EI): m/z calcd for C18H16N2:260.13135 [M]+ ; found: 260.1327.

2,2’’-Diiodo-[1,1’:4’,1’’]terphenyl (2,2’’-DITP): Sodium nitrite (1.8 g,26.1 mmol) dissolved in water (72 mL) and cooled at 0 8C was added se-quentially over 15 min to a stirred solution of compound 7 (2.7 g,10.4 mmol) suspended in water (135 mL) containing concentrated hydro-chloric acid (38 mL) at 0 8C. The clear yellow solution was stirred for 1 hat 0 8C (solution 1). In a separate vessel, a solution of potassium iodide(17.4 g, 104.8 mmol) in water (190 mL) was cooled to 0 8C (solution 2).Solution 1 was added to solution 2 over 10 min at 0 8C and the dark redsolution was stirred for a further 1 h at 0 8C. The ice bath was removedand the mixture was stirred at room temperature for 2 h and then heatedto 60 8C for a further 2.5 h. The resulting mixture was stirred at roomtemperature overnight and extracted with dichloromethane (5R100 mL).The organic layers were washed with water, dried (MgSO4) and the sol-vent was removed in vacuo. The red crude product was purified bycolumn chromatography on silica gel eluting first with light petroleumand second with dichloromethane/light petroleum (1:9). After removal ofthe solvents, crystallisation (light petroleum) afforded compound 2,2’’-DITP (3.0 g, 63%) as a colourless solid. M.p. 156 8C (light petroleum)(lit. [59]; m.p. 158.9 8C (ethanol)); 1H NMR (300 MHz; CDCl3): d=7.98(d, J=7.5 Hz, 2H; ArH), 7.42–7.39 (m, 8H; ArH), 7.08–7.03 ppm (m,2H; ArH); 13C NMR (75 MHz; CDCl3): d=146.2 (C), 143.3 (C), 139.6(CH), 130.1 (CH), 128.84 (CH), 128.81 (CH), 128.1 (CH), 98.5 ppm ACHTUNGTRENNUNG(C-I); IR (KBr): n =3060, 3038, 1929, 1911, 1800, 1583, 1555, 1458, 1424,1391, 1250, 1005, 999 cm�1; HRMS (EI): m/z calcd for C18H12I2:481.90285 [M]+ ; found: 481.9027; elemental analysis calcd (%) forC18H12I2: C 44.8, H 2.5; found: C 44.4, H 2.5.

9-[1,1’:4’,1’’]Terphenyl-2’’-yl-9H-fluoren-9-ol (11): Mono alcohol deriva-tive 11 was obtained as a byproduct during the coupling of the 9-fluor-ACHTUNGTRENNUNGenone and 2,2’’-DITP. M.p. 123.5 8C; 1H NMR (300 MHz; CDCl3) d=

8.51 (d, J=7.5 Hz, 1H; ArH), 7.64–7.11 (m, 15H; ArH), 6.97 (d, J=

7.5 Hz, 1H; ArH), 6.81 (d, J=8.3 Hz, 2H; ArH), 6.06 (d, J=8.3 Hz, 2H;ArH), 2.46 ppm (br s, 1H; OH); 13C NMR (75 MHz; CDCl3): d=150.6,148.8, 141.5, 141.4, 141.3, 140.6, 140.3, 140.1, 139.6, 139.4, 137.8, 131.0,129.2, 128.8, 128.7, 127.9, 127.2, 126.9, 126.3, 124.9, 124.4, 123.5, 120.0,119.9, 82.41 ppm; HRMS (EI): m/z calcd for C31H22O: 410.16707 [M]+ ;found: 410.1691.

Spectroscopic studies : UV/Vis spectra were recorded using a UV/Visiblespectrophotometer UVIKON XL Biotech. The optical band gap was cal-culated from the absorption edge of the UV/Vis absorption spectra byusing the formula DEopt (eV)=hc/l in which l is the absorption edge (inm). With h=6.6262R10�34J s (1 eV=1.602R10�19 J) and c=2.99R108 ms�1, this equation may be simplified as: DEopt (eV)=1237.5/l (l innm). Photoluminescence spectra were recorded at room temperaturewith a PTI spectrofluorimeter (PTI-814 PDS, MD 5020, LPS 220B) usinga xenon lamp. Quantum yields (fsol) were calculated relative to quininesulfate (fsol =0.546 in H2SO4 1n) using standard procedures.[72] fsol wasdetermined according to the following Equation (1), in which subscripts sand r refer to the sample and reference, respectively. The integrated areaof the emission peak in arbitrary units is given as T, n is the refractingindex of the solvent (ns =1.42662 for cyclohexane and 1.469 for decalin;nr=1.3325) and A is the absorbance. The emission spectra of DSF-IF,DSF-IF(iPr)2, DSF-IF(oct)2, SBF and F were recorded in solution in cy-clohexane and IF in solution in decalin. IR spectra were recorded on aBIORAD IRFTS175C.

�sol ¼ �ref � 100� Ts Ar

Tr As

�ns

nr

�2

ð1Þ

www.chemeurj.org L 2007 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim Chem. Eur. J. 2007, 13, 10055 – 1006910066

C. Poriel, J. Rault-Berthelot, L. Vignau et al.

Thermal analysis : Thermogravimetric analyses (TGA) were performedwith a Rigaku Thermoflex instrument under a nitrogen atmosphere.TGA measurements were carried out between 40 and 600 8C with a heat-ing rate of 40 8Ch�1 for IF and SBF and 5 8Cmin�1 for DSF-IFs. DSCmeasurements were carried out on a DSC 2010 TA instrument between50 to 350 8C at a rate of 10 8Cmin�1 for DSF-IFs and at a rate of40 8Cmin�1 for SBF and IF. Melting points were determined by using anelectrothermal melting-point apparatus or by DSC.

Electrochemical studies : All electrochemical experiments were per-formed using a Pt disk electrode (diameter 1 mm), the counter electrodewas a vitreous carbon rod and the reference electrode was a silver wirein a solution of AgNO3 in CH3CN (0.1m). Ferrocene was added to theelectrolyte solution at the end of a series of experiments. The ferrocene/ferrocenium (Fc/Fc+) couple served as internal standard and all reportedpotentials were referenced to its reversible formal potential. All solventswere purchased from SDS with less than 100 ppm of water and storedunder Argon. Activated Al2O3 was added in the electrolytic solution toremove excess moisture. The three-electrode cell was connected to aPAR Model 173 potentiostat monitored with a PAR Model 175 signalgenerator and a PAR Model 179 signal coulometer. The cyclic voltamme-try traces (CVs) were recorded on an XY SEFRAM-type TGM 164. Fora further comparison of the electrochemical and optical properties, allpotentials are referred to the SCE electrode that was calibrated at�0.405 V versus Fc/Fc+ system in CH2Cl2. The peak potentials are givenwith an error of 20 mV corresponding to 1 mm on the XY-Sefram re-cording table. Chemicals for electrochemistry: acetonitrile with less than5% of water (ref. SDS 00610S21) and dichloromethane with less than100 ppm of water (ref. SDS 02910E21) were used without purification.Tetrabutylammonium hexafluorophosphate from FLUKA was used with-out purification. Aluminum oxide was obtained from WoVlm, activatedby heating at 300 8C under vacuum for 12 h and used at once underargon pressure.

X-ray structure determination : Crystal data and structure refinements for2,2’DITP: C18H12I2, Mr 482.08, crystal size 0.1R0.1R0.1 mm, colourlessprism, orthorhombic, space group Pbca, T=93(2) K, a=11.2215(18), b=

8.0151(12), c=16.796(3) Q, V=1510.7(4) Q3, Z=4, 1calcd =2.120 Mgm�3,m(MoKa)=4.150 mm�1, 8697 measured reflections, 1315 independent re-flections (Rint)= (0.0683), final R1=0.0473, wR2=0.1007 for 981 ob-served reflections [I>2s(I)]. Crystal data and structure refinements for11: C31H22O, Mr 410.49, crystal size 0.1R0.1R0.01 mm, colourless platelet,orthorhombic, space group Pbca, T=173(2) K, a=14.901(2), b=

8.2947(12), c=35.765(5) Q, V=4420.6(11) Q3, Z=8, 1calcd =1.234 Mgm�3,m (CuKa)=0.562 mm�1, 19222 measured reflections, 1707 independent re-flections (Rint)= (0.1798), final R1=0.0780, wR2=0.1832 for 1233 ob-served reflections [I>2s(I)]. Crystal data and structure refinements forDSF-IF(iPr)2: C31H22O, Mr 410.49, crystal size 0.18R0.18R0.1 mm, colour-less prism, monoclinic, space group P21, T=93(2) K, a=9.7998(7), b=

14.8143(11), c=15.1839(12) Q, V=2111.6(3) Q3, Z=2, 1calcd =

1.380 Mgm�3, m(MoKa)=0.444 mm�1, 13187 measured reflections, 5575independent reflections (Rint)= (0.0153), final R1=0.0236, wR2=0.0623for 5556 observed reflections [I>2s(I)]. CCDC 653146, 653147 and653148 contain the supplementary crystallographic data for this paper.These data can be obtained free of charge from The Cambridge Crystal-lographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

EL fabrication and testing : OLEDs were fabricated using the followingprocedure.[103] Indium–tin oxide (ITO) substrates on glass from Merckunderwent a solvent ultrasonic cleansing by using acetone and isopropan-ACHTUNGTRENNUNGol followed by a 15 min UV-ozone treatment. A layer of poly(3,4-ethyl-ene dioxythiophene) doped with poly(styrene sulfonate) (PEDOT/PSSfrom HC Starck) was then deposited onto ITO by spin-coating at5000 rpm, from a 3 wt% water dispersion to form a 40 nm thick layer.PEDOT/PSS was subsequently annealed at 80 8C under vacuum for30 min. This layer improves hole injection from the ITO to the HOMOlevel of the organic material and increases the performances and the life-time of the device.[104] Then, the DSF-IF layer was thermally evaporatedunder vacuum (ca. 10�6 mbar) at a low deposition rate of 0.1 nms�1. Thelayer thickness was monitored in situ by a piezoelectric quartz balanceduring the evaporation. Calcium cathodes were finally evaporated

through a shadow mask. The OLEDs were then stored and characterisedunder inert atmosphere in a nitrogen glove box ([O2] and [H2O]<1 ppm). Contacts on ITO and Ca were taken using a probe (Karl SussPM5). Current–voltage–luminance (I-V-L) curves were recorded using aKeithley 4200 SCS. Light emission was collected using a calibrated pho-todiode. Electroluminescence spectra were measured with a CCD spec-trometer (Ocean Optics HR 2000).

Acknowledgements

The authors would like to thank the CINES (Centre Informatique Na-tional delXEnseignement SupDrieur, Montpellier) for awarding of comput-ing time, the C.R.M.P.O (Centre RDgional de Mesure Physique delXOu-est) for high-resolution mass measurements and for CHN analysis. Wealso thank Dr. Muriel Hissler for helpful discussions and her help influor ACHTUNGTRENNUNGescence measurements and Stephanie Fryars for technical assistance.

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Received: July 5, 2007Published online: November 19, 2007

Chem. Eur. J. 2007, 13, 10055 – 10069 L 2007 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim www.chemeurj.org 10069

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